Known in the art are various methods for preparing sterically hindered bisphenols of polyphenols. For example, currently used is a method for preparing 2,2'-methylene-bis-(4-methyl-6-tert.butylphenol), wherein the desired product is prepared by alkylation of 4-methylphenol with isobutylene in the presence of a catalyst, followed by separation and condensation of the resulting 2-tert.butyl-4-methylphenol with formaldehyde.
Condensation is conducted in the presence of acidic catalysts such as sulphuric acid. The process is carried out in an aqueous emulsion containing a surfactant and an organic solvent at a temperature within the range of from 75.degree. to 90.degree. C.
This prior art method has a disadvantage residing in the complicated technology of the process.
The process is performed in two stages, a great amount of waste water is formed (about 30 m.sup.3 per ton of the product) which is contaminated with surfactants and organic solvents. Besides, as the starting product in the process use is made of p-cresol which is a difficult material to obtain.
Due to p-cresol being a critical product, another method for the preparation of 2,2'-methylene-bis-(4-methyl-6-tert.butylphenol) from 2,6-ditert.butyl-4-methylphenol has been developed, based on the production of the latter rather readily from cheap and easily available phenol. The process is based on dealkylation of 2,6-ditert.butyl-4-methylphenol, followed by separation and condensation of the resulting 2-tert.butyl-4-methylphenol with formaldehyde.
One of the principal disadvantages of this method also resides in the formation of a great amount of acidic waste water containing surfactants and organic solvents. Purification of such waste water on a commercial scale is rather complicated and economically inefficient.
Also known in the art is a method for preparing 2,2'-methylene-bis(4-methyl-6-tert.butylphenol) which has certain advantages over the methods mentioned hereinabove, since it makes possible to eliminate the formation of waste water. According to this method, the desired product is obtained from 2,6-ditert.butyl-4-methylphenol in two stages, namely: dealkylation of 2,6-ditert.butyl-4-methylphenol, followed by separation and condensation of the resulting 2-tert.butyl4-methylphenol with an acetal in the presence of an acidic catalyst at a temperature within the range of from 30.degree. to 140.degree. C.
This prior art process as well as those described hereinbefore are performed in two stages and require separation, in a pure form, of 2-tert.butyl-4-methylphenol having a strong unpleasant odor, high toxicity and volatility. Furthermore, a complicated process technology is required to perform all the above-discussed prior art methods.
Moreover, the prior art methods described hereinbefore make it possible to prepare only bisphenols. As regards polyphenols, known in the art are complicated multi-staged methods of preparing same. For example, polyphenols are prepared by reacting para-alkylphenols having with free ortho-positions with chloromethyl derivatives of 2,6-dialkylphenols according to the following scheme: ##STR6##